One of the first responses to a cold stress is an overt oscillation which has been called shiver. Shiver bears some striking resemblances to other kinds of overt tremors but has not been quantitatively studied in-depth. The purpose of the research is to investigate the properties of shiver and to then contrast it to another tremor called physiological action tremor. The acute studies will be done using human subjects to monitor the onset, duration and magnitude of the electromyograms recorded from various parts of the body exposed to come (30F) air. The relationship between this oscillation seen during cold exposure (shiver) and that seen during normal slow voluntary movement (action tremor) will be compared using spectral and cross correlation techniques. In addition, the duration of the on-off burst associated with these oscillations will be studied to investigate whether they share the same temporal characteristics. Both of these oscillations will be investigated to see if their characteristics can be modified by sensory input (e.g., weights and local anesthetic). The role that motor units and muscle receptors play in these oscillations will be studied using the decerebrate cat preparation. The motor response to cold is an important defense mechanism against cold stress. Additional information is required to understand its genesis and maintenance relative to generating an adequate core temperature. In elderly individuals this mechanism might be blunted so that they cannot effectively generate enough heat. In addition to this aspect, this proposed research is investigating whether shivering and other overt tremors might share a common motor system and whether different stimuli might activate this common system. If such was the case, then the understanding of this common oscillating system would be significant in the treatment of those diseases that might also use this oscillating system, e.g., Parkinsonism.